You can't replace Direct3d with OpenGL because it's part of your computer. However you can run OpenGL programs or games by downloading and installing a program called GLDirect. This program allows you to run OpenGL-based games and other applications using your graphics card's DirectX drivers.

1. Direct3D is a proprietary API designed by Microsoft Corporation for hardware 3D acceleration on the Windows platform

2. OpenGL is an open standard API that provides a number of functions for the rendering of 2D and 3D graphics and is available on most modern operating systems. If hardware 3D acceleration is present, OpenGL can use it.

Vertex and pixel (or fragment) shaders are shaders that run on a graphics card, executed once for every vertex or pixel in a specified 3D mesh. They operate in the context of interactively rendering a 3D scene, usually using either the Direct3D or OpenGL API.

I want to draw stippled lines by openGL so how I can

ok